Exhaust manifold

ABSTRACT

An exhaust manifold includes a head flange member, a plurality of branch pipe parts and a collector pipe part. The head flange member has a flange main body portion and a cylinder head mounting surface configured and arranged to be attached to a cylinder head of an engine. Each of the branch pipe parts has an upstream end portion with respect to an exhaust gas flow fixed to one side of the head flange member that is opposite from the cylinder head mounting surface. The collector pipe part is connected to a downstream end portion with respect to the exhaust gas flow of each of the branch pipe parts. An area of the cylinder head mounting surface is smaller than a cross sectional area of the head flange main body portion taken along a plane substantially parallel to the cylinder head mounting surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2012-051413, filed on Mar. 8, 2012. The entire disclosure of JapanesePatent Application No. 2012-051413 is hereby incorporated herein byreference.

BACKGROUND

1. Field of the Invention

The present invention relates to an exhaust manifold that that isattached to a cylinder head of an internal combustion engine and allowsexhaust gas to pass through.

2. Background Information

Japanese Laid-Open Patent Application No. 2004-52715 presents a knownconventional exhaust manifold. This conventional exhaust manifold has ahollow dual pipe structure comprising an inner pipe covered by an outerpipe. A head flange is fixed to one end of each of the branch pipes ofthe inner pipe, and the other ends of the inner pipes are connected to acollector inner pipe. The head flange has through holes provided betweenadjacent branch pipes, and a flat surface of the head flange located onthe opposite side as the branch pipes is attached to the cylinder headof an engine (internal combustion engine) such that the openings of thebranch pipes are aligned with the exhaust ports of the cylinder head.

SUMMARY

With the conventional exhaust manifold explained above, since thecylinder head is constantly cooled with circulating cooling water andthe head flange is fastened to the cylinder head, the head flange of theexhaust manifold looses heat to the cylinder head and is cooled.Meanwhile, the inner pipes of the branch pipes and the outer pipescovering the inner pipes are at a high temperature becausehigh-temperature exhaust gas flows through the inner pipes and thebranch pipes are not cooled by cooling water or the like. Consequently,a large temperature difference exists between the head flange and theouter pipe and inner pipe connected to the head flange and a differencebetween an elongation or expansion amount of the head flange in alengthwise direction caused by heat and an elongation amount of theinner and outer pipes in a lengthwise direction caused by heat becomeslarge.

The present invention was conceived in view of the problem justexplained and its object is to provide an exhaust manifold that canprevent the durability of the exhaust manifold from declining due to adifference of thermal expansion between the head flange and the innerand outer pipes.

An exhaust manifold according to one aspect includes a head flangemember, a plurality of branch pipe parts and a collector pipe part. Thehead flange member has a flange main body portion and a cylinder headmounting surface configured and arranged to be attached to a cylinderhead of an engine. Each of the branch pipe parts has an upstream endportion with respect to an exhaust gas flow fixed to one side of thehead flange member that is opposite from the cylinder head mountingsurface. The collector pipe part is connected to a downstream endportion with respect to the exhaust gas flow of each of the branch pipeparts. An area of the cylinder head mounting surface is smaller than across sectional area of the head flange main body portion taken along aplane substantially parallel to the cylinder head mounting surface.

With this arrangement, a contact surface area between the cylinder headand the mounting surface of the head flange member that contacts thecylinder head is smaller than the cross sectional area of the headflange main body portion. Consequently, the amount of heat transferredfrom the head flange to the cooled cylinder head is small and the headflange can be maintained at a higher temperature. As a result, thedifference between the thermal expansion amounts of the head flange andthe branch pipe parts can be reduced and the durability of the exhaustmanifold can be improved.

In the exhaust manifold as described above, a surface of the flange mainbody portion and the cylinder head mounting surface are preferablyconnected with a step-shaped level difference in-between. With thisarrangement, the contact surface area between the cylinder head and themounting surface of the head flange member can be made smaller than thecross sectional area of the head flange main body with a simple andinexpensive method.

In the exhaust manifold as described above, the head flange memberpreferably defines a through hole in a position that avoids the branchpipe parts. With this arrangement, the contact surface area with respectto the cylinder head can be reduced further and the difference betweenthe thermal expansion amounts of the head flange and the branch pipescan be reduced further.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the attached drawings which form a part of thisoriginal disclosure:

FIG. 1 is a perspective view of an exhaust manifold according to oneembodiment of the present invention.

FIG. 2 is a frontal plan view of a head flange member of the exhaustmanifold according to the embodiment.

FIG. 3 is a cross sectional view of the head flange member taken along asection line S1-S1 shown in FIG. 2.

FIG. 4 is a cross sectional view of the head flange member taken along asection line S2-S2 shown in FIG. 2.

DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to thedrawings. It will be apparent to those skilled in the art from thisdisclosure that the following descriptions of the embodiments areprovided for illustration only and not for the purpose of limiting theinvention as defined by the appended claims and their equivalents.

The overall constituent features of the exhaust manifold according toone embodiment will now be explained based on FIG. 1. The exhaustmanifold 2 according to the embodiment is attached to a side face of acylinder head 1 a of an engine 1 comprising an internal combustionengine using bolts (not shown).

The exhaust manifold 2 comprises a head flange member 20, a thin-walledinner pipe (not shown) including a plurality of inner branch pipes (fourin this embodiment) and an inner collector pipe (not shown) connected tothe inner branch pipes, a thick-walled outer pipe 3 that covers theinner pipe such that a gap exists between the outer circumference of theinner pipe and the inner circumference of the outer pipe 3, and a spacer(not shown). For example, a hollow dual-pipe structure disclosed inJapanese Laid-Open Patent Application No. 2004-52715 may be utilized toform the inner branch pipes, the collector pipe and the outer pipe 3 ofthis embodiment.

The head flange member 20 has a flange main body portion 2 a having acylinder head mounting surface that is fixed to the cylinder head 1 aand a surface that is fixed by welding to exhaust gas upstream endportions of the inner pipe and the outer pipe. A plurality of exhaustgas flow holes (four in this embodiment) are provided in the flange mainbody portion 2 a in positions aligned with exhaust ports formed in thecylinder head 1 a. The structure of the head flange member 20 will beexplained in more detail below.

The inner pipe is inside the outer pipe 3 and cannot be seen in FIG. 1.The inner pipe has four branch inner pipes and a collector inner pipe.The exhaust gas upstream end portions of the branch inner pipes aresecurely attached by welding to the head flange member 20 such that theyare aligned with the positions of the exhaust ports. The exhaust gasdownstream end portions of the branch pipes are connected to an exhaustgas upstream end portion of the collector inner pipe. An exhaust gasdownstream end portion of the collector inner pipe bends downward fromone location on an undersurface.

The outer pipe 3 comprises branch outer pipes 3 a to 3 d that cover thefour branch inner pipes from the outside such that a gap existsin-between, a collector outer pipe 3 e that covers the collector innerpipe from the outside such that a gap exits in-between, and an exhaustouter pipe portion 3 f that covers the downwardly bent exhaust gasdownstream end portion of the collector inner pipe from the outside suchthat a gap exists in-between. Spacers are disposed between the outerpipe 3 and the inner pipe in several locations to maintain the gaps. Thespacers are made of for example, a metal mesh.

The branch inner pipe and/or the branch outer pipes 3 a to 3 dcorrespond to the branch pipe parts of this embodiment, and thecollector inner pipe and/or the collector outer pipe 3 e correspond tothe collector pipe part of this embodiment.

The structure of the head flange member 20 will now be explained in moredetail based on FIGS. 2 to 4. FIG. 2 is a frontal view of the headflange member 20 as seen from the surface of the cylinder head 1 a ontowhich the head flange member 20 mounts. In FIG. 2, the cylinder headmounting surface is shown with hatching. FIG. 3 is a cross sectionalview taken along the section line S1-S1 of FIG. 2. The upper side inFIG. 3 is the mounting surface side that attaches to the cylinder head 1a, and the lower side is the side having the surface that attaches tothe inner pipe and the outer pipe 3. FIG. 4 is a cross sectional viewtaken along the section line S2-S2 of FIG. 2. The upper side in FIG. 4is the mounting surface side that attaches to the cylinder head 1 a, andthe lower side is the side having the surface that mates with the innerpipe and the outer pipe 3.

As shown in FIGS. 2 to 4, the head flange member 20 has a plate-shapedflange main body portion 2 a, portions 21 a to 21 d located on one sideof the flange main body portion 2 a, i.e., the side having the surfacethat attaches to the cylinder head 1 a, and a portion 25 located on theother side of the flange main body portion 2 a, i.e., the side havingthe surface that attaches to the inner pipe and the outer pipe 3 on theopposite side of the flange main body portion 2 a as the surface thatattaches to the cylinder head 1 a.

The portions 21 a to 21 d on the side having the cylinder head mountingsurface that attaches to the cylinder head 1 a correspond to portionsindicated with hatching in FIG. 2, and, as shown in FIGS. 3 and 4, areconfigured to protrude toward the cylinder head 1 a from the flange mainbody portion 2 a such that a step-shaped level difference exists betweenthe portions 21 a to 21 d and the flange main body portion 2 a. In otherwords, the cylinder head mounting surface of the portions 21 a to 21 dis disposed outwardly of a surface of the flange main body portion 2 awhen viewed along a direction parallel to the cylinder head mountingsurface as shown in FIG. 2. The height of the step-shaped leveldifference is set to 1 mm in this embodiment, but it is acceptable toset a different height. As illustrated in FIG. 2, the cylinder headmounting surface or the contact surface area (area of the hatchedportions in FIG. 2) between the cylinder head 1 a and the surfaceportions 21 a to 21 d on the cylinder head side of the flange main bodyportion 2 a is much smaller than the cross sectional surface area of theflange main body portion 2 a and the surface area of the portion 25 onthe pipe side of the flange man body portion 2 a. As used herein, thecross sectional surface area of the flange main body portion 2 a refersto a cross sectional surface area of the plate-shaped flange main bodyportion 2 a as taken along a plane substantially parallel to thecylinder head mounting surface (i.e., a horizontal plane in FIG. 3).

The portions 21 a to 21 d on the cylinder head side comprise portionsthat surround the peripheries of four exhaust gas inlet holes 22 a to 22d formed to correspond to the four exhaust ports provided in thecylinder head 1 a and portions that surround the peripheries of eightbolt holes 23 a to 23 d through which bolts are inserted to mount themanifold to the cylinder head 1 a. The pair of bolt holes 23 a, 23 b, 23c, 23 d corresponding to each of the exhaust ports is positioneddiagonally with respect to a line joining the centers of the exhaustports. The portions 21 a to 21 d on the side having the surface thatattaches to the cylinder head 1 a are configured to be independententities corresponding to each of the exhaust ports, and adjacentportions 21 a to 21 d do not join each another directly.

Meanwhile, the flange main body portion 2 a has a cross sectionalsurface area larger than the other portions 21 a to 21 d and 25, and atotal of three through holes 24 a, 24 b, and 24 c are formed betweenadjacent holes of the four exhaust gas inlet holes 22 a to 22 d. Thethrough holes 24 a, 24 b, and 24 c provided to further reduce thesurface area of the head flange member 20 that contacts the cylinderhead 1 a.

Four recesses for attaching to the inner pipe and the outer pipe 3 areformed in the portion 25 on the side having the surface that attaches tothe inner pipe and the outer pipe 3 in positions corresponding theexhaust ports. The inner pipe and the outer pipe 3 are arranged suchthat the exhaust gas upstream end portions are inserted into theserecesses and the head flange member 20 is welded to the inner pipe andouter pipe 3. Thus, the surface area of the portion 25 on the pipe sideis smaller than the cross sectional surface area of the flange main bodyportion 2 a but slightly larger than the contact surface area of theportions 21 a to 21 d on the cylinder head side.

With the exhaust manifold 2 configured as explained heretofore, theexhaust gas discharged from the cylinders of the engine 1 exits theexhaust ports of the cylinder head 1 a, passes through the exhaust gasinlet holes 22 a to 22 d of the flange main body portion 2 a, and flowsto into the branch inner pipes. The exhaust gas that flows into thebranch inner pipes enters the collector inner pipe and is combined intoa single flow passage before discharged downward from the exhaust gasdownstream end portion. When the exhaust gas flows through the innerpipes, the outer pipe 3 serves to suppress the temperature drop of theexhaust gas in the inner pipes.

A catalytic converter is provided downstream of the exhaust manifold,and exhaust gas exiting the exhaust manifold activates the cleaningeffect of the catalytic converter because it has been held at a hightemperature in the exhaust manifold. As a result, the exhaust gascleaning effect is accelerated. Downstream of the catalytic converter,the exhaust gas passes through an exhaust pipe and a muffler beforebeing released to the outside of the vehicle.

During the operation explained above, the inner pipe and the outer pipe3 of the exhaust manifold are at a high temperature due to thehigh-temperature exhaust gas. Meanwhile, the head flange member 20 ofthe exhaust manifold looses heat to the cylinder head 1 a because asurface on one side of the head flange member 20 contacts the cylinderhead 1 a, which is constantly cooled by cooling water while the engine 1is running.

However, in the exhaust manifold according to the embodiment, thecontact surface area between the one surface of the head flange member20 and the cylinder head 1 a is slightly smaller than the crosssectional surface area of the flange main body portion 2 a. Consequentlythe amount of heat lost is small. As a result, the head flange member 20can be held at a higher temperature and, thus, parts of the exhaustmanifold can be prevented from becoming damaged due to a concentrationof strain caused by a difference of thermal expansion.

The effects obtainable with the exhaust manifold according to theembodiment will now be reiterated. With the exhaust manifold accordingto the embodiment, the contact surface area between the surface on theone side of the head flange member 20 and the cylinder head 1 a isslightly smaller than the cross sectional surface area of the flangemain body portion 2 a. Consequently, the temperature decrease of thehead flange member 20 resulting from contact with the cylinder head 1 acan be suppressed. Thus, the parts of the exhaust manifold can beprevented from being damaged due to a concentration of strain caused bya difference of thermal expansion.

Since the aforementioned difference of surface areas can be obtained byconfiguring the head flange member 20 such that the portions on the sidehaving the surface that attaches to the cylinder head 1 a join theflange main body portion 2 a through a step-shaped level difference,that is, by removing portions other than the portions on the side havingthe surface that attaches cylinder head 1 a side from the flange mainbody portion 2 a, the head flange member 20 can be fabricated easily andinexpensively.

Since the head flange member 20 has through holes 20 a to 20 c inpositions that avoid the branch inner pipes and the outer pipe, thecontact surface area between the head flange member 20 and the cylinderhead 1 a can be reduced further and the temperature decrease of the headflange member 20 can be suppressed further.

Although the present invention is explained based on the embodiments,the present invention is not limited to these embodiments. The presentinvention includes design changes that do not depart from the scope ofthe invention.

For example, although the engine 1 is a four-cylinder type, theinvention is not limited to a four-cylinder engine and a six-cylinderengine is also acceptable. The exhaust manifold according to theillustrated embodiment has a hollow dual-pipe structure, but theinvention is not limited to such a structure.

Also, the shape of the head flange member 20 and the shapes of theportions on the side of the head flange member 20 having the surfacethat attaches to the cylinder head can be different from the embodiment.

General Interpretation of Terms

In understanding the scope of the present invention, the term“comprising” and its derivatives, as used herein, are intended to beopen ended terms that specify the presence of the stated features,elements, components, groups, integers, and/or steps, but do not excludethe presence of other unstated features, elements, components, groups,integers and/or steps. The foregoing also applies to words havingsimilar meanings such as the terms, “including”, “having” and theirderivatives. Also, the terms “part,” “section,” “portion,” “member” or“element” when used in the singular can have the dual meaning of asingle part or a plurality of parts. The terms of degree such as“substantially”, “about” and “approximately” as used herein mean areasonable amount of deviation of the modified term such that the endresult is not significantly changed.

While only selected embodiments have been chosen to illustrate thepresent invention, it will be apparent to those skilled in the art fromthis disclosure that various changes and modifications can be madeherein without departing from the scope of the invention as defined inthe appended claims. For example, the size, shape, location ororientation of the various components can be changed as needed and/ordesired. Components that are shown directly connected or contacting eachother can have intermediate structures disposed between them. Thefunctions of one element can be performed by two, and vice versa. Thestructures and functions of one embodiment can be adopted in anotherembodiment. It is not necessary for all advantages to be present in aparticular embodiment at the same time. Every feature which is uniquefrom the prior art, alone or in combination with other features, alsoshould be considered a separate description of further inventions by theapplicant, including the structural and/or functional concepts embodiedby such feature(s). Thus, the foregoing descriptions of the embodimentsaccording to the present invention are provided for illustration only,and not for the purpose of limiting the invention as defined by theappended claims and their equivalents.

What is claimed is:
 1. An exhaust manifold comprising: a head flangemember having a flange main body portion and a cylinder head mountingsurface configured and arranged to be attached to a cylinder head of anengine; a plurality of branch pipe parts with each of the branch pipeparts having an upstream end portion with respect to an exhaust gas flowfixed to one side of the head flange member that is opposite from thecylinder head mounting surface; and a collector pipe part connected to adownstream end portion with respect to the exhaust gas flow of each ofthe branch pipe parts, an area of the cylinder head mounting surfacebeing smaller than a cross sectional area of the head flange main bodyportion taken along a plane substantially parallel to the cylinder headmounting surface.
 2. The exhaust manifold according to claim 1, whereina surface of the flange main body portion and the cylinder head mountingsurface are connected with a step-shaped level difference in-between. 3.The exhaust manifold according to claim 1, wherein the head flangemember defines a through hole in a position that avoids the branch pipeparts.
 4. The exhaust manifold according to claim 1, wherein thecylinder head mounting surface is disposed outwardly of a surface of theflange main body portion when viewed along a direction parallel to thecylinder head mounting surface.